1. Field of the Invention
This invention relates to a moldable putty for use in medical applications for the augmentation of the replacement of hard and soft tissue. More specifically, this invention relates to a composite comprised of a polymer that is moldable at "hot water" temperatures, retains its shape at temperatures substantially below that range, and may include tissue growth augmentation materials.
2. Background of the Prior Art
It has long been known that the replacement or regeneration of supportive and connective tissue, particularly hard tissue such as bone materials, may be augmented by the presence or application of various organic and inorganic materials. Thus, U.S. Pat. No. 4,440,750, describes in detail a wide number of compounds found to be osteogenic, and describes a method and preparation for introducing such osteogenic materials where it is necessary to enhance or promote bone regeneration, such as in the case, of genetic disorders and traumatic injury.
Similarly, a large number of tissue augmentation compositions are known, that comprise soft or moldable polymeric materials, which are designed to occupy the space where tissue regeneration is desired, and eventually be replaced by the hard or soft regenerated tissue, such as cartilage or bone. Among the references directed to such invention are U.S. Pat. Nos. 4,424,208 and 4,347,234. The latter, in particular, describes a collagen-based shaped mass which may include osteogenic material, such as tricalcium phosphate. The implant material of both U.S. Pat. Nos. 4,424,208 and 4,347,234 is based on collagen in a binder to form a polymeric mass.
A similar material is provided through an alternative approach in U.S. Pat. No. 3,949,073. That patent describes a collagen-based solution which may be injected or implanted into the desired location, and immediately polymerized into a stable mass upon injection. The reference also suggests the use of tissue augmentation materials in addition to the collagen polymer.
A different approach to the replacement of bone tissue is taken in U.S. Pat. No. 3,919,773, which is directed to a bone replacement, or implant, particularly designed for use in dental or oral surgery, where a socket is exposed after tooth extraction, or an similar void is formed in dental bone. Accordingly, a polymerizable material, comprised, in contrast to U.S. Pat. No. 3,949,073, of synthetic polymers, is injected into the socket and rapidly polymerizes therein, to form a hardened, permanent fixture. To enhance subsequent tissue connection, but not replacement, to the implant, the material, prior to polymerization, is provided with discrete particles that are soluble in body fluids commonly encountered in the oral cavity. When these particles are dissolved, the implant is made porous, which enhances the connection of connective tissue thereto.
Also generally known in the art are purely synthetic polymers useful, in general, as surgical articles or devices, owing to their complete bioabsorbability. Thus, U.S. Pat. No. 4,243,775 describes a polymer based on lactide and glycolide, which, when polymerized, is designed as a medical suture, or similar sterile surgical article. However, the polymer of the reference is not moldable, and is not suggested as being suitable for the enhancement of, or replacement by, connective tissue.
Other related art also includes a variety of hemostatic materials, designed to control osseous hemorrhage, particularly in the case of orthopedic surgery or the like. Several different compositions are generally described in U.S. Pat. Nos. 4,439,420; 4,440,789 and 4,443,430. Although these compositions are useful in the healing process, and a necessary adjunct to surgical or traumatic injury to bone and similar connective tissue, they do not serve as "scaffolds" or similar basis for the replacement of the implant by regenerated tissue, nor do they substantially promote to the regeneration of that tissue.
All of the above-described medical articles and compositions suffer from one or more disadvantages in the provision of a medical putty which may be used as a temporary form for the augmentation of hard or soft connective tissue, both by replacement of the implant with regenerated tissue, and delivering an osteogenic material. Those compositions which are not moldable prior to insertion in the body of the patient present the extreme problem that the space, gap or void cannot be completely filled, or the scaffold cannot be designed or molded in the desired shape for eventual replacement by hard or soft tissue. This is particularly true of compositions designed to be polymerizable in situ, which offer only the possibility of filling the entire void or cavity with the implant.
Although the compositions based on collagen and including osteogenic materials, and designed to be molded outside the body, such as those of U.S. Pat. No. 4,347,234, present an alternative to the in situ polymerization methods, the reliance on a collagen-based polymer presents its own problems. Specifically, collagen is, although generally biocompatible, not completely biodegradable or resorbable, such that the implant remains for a long period of time in the wound area, being surrounded, but not absorbed, by the regenerating tissue. Additionally, collagen, being an organic substance principally derived from bovines, presents potentially serious allergenic reaction problems, and general difficulties with the patient's immune system. Further, it is difficult to insure the sterility of collagen, and the storage requirements associated therewith are quite extensive, and expensive. A further disadvantage presented by the use of collagen or collagen-based polymers is the moldability of the polymer. Although it is desirable for the polymer to be moldable outside the body, once inserted, the polymer should be preferably be resistant to permanent changes in shape through applied pressure, particularly where oral or dental surgery is involved. Thus, after implantation or substitution for mandibular or maxillary bone loss during oral surgery, it may be desirable or necessary for the patient to resume chewing, etc. The pressure and stress applied by these activities will deform an implant that remains moldable after implantation, and destroy, or at least detract from, the value and utility of the implanted article.
Accordingly, there continues to be a need for a stable but moldable implant material suitable for use in soft and hard tissue regeneration and replacement.